large batterybank - small solar system

tef Registered Users Posts: 2

I have a small offgrid solar system consisting of 2x 190Ah lead acid batteries connected in parallel to get 12V 380Ah.
I charge the bank with solar panels mounted on a dual axis tracker with about 400-500W form moring to evening on a sunny day.

Now I got 18x 150Ah UPS Batteries for free. I know that this amount of capacity is many times too much for my solar panels but the batteries seem to be in a good condition, so I really had to take them.

My plan is to connect them all in parallel and use less than 5% of the total Ah a day to get them charged on a regular basis.
I would not exeed this limit because there is a connection to the grid and I don't rely on batterypower.

In the next few weeks I will get additional solar panels. Then I will switch to 24V as soon as possible.

Do you recommend connecting all 18 batteries in parallel as mentionend above or would it be better to use only a few of them and charge the rest seperately up to the moment I have extended my setup.

Sorry for my bad english.

thanks in advance


  • Brock
    Brock Solar Expert Posts: 639 ✭✭✭✭
    Re: large batterybank - small solar system

    I would put them in two groups of 9 or three groups of 6. Otherwise the solar panels you have won't be able to push them up to their "full" voltage. Although even in two or three groups you still may not have enough solar power to get them fully charged.
    3kw solar PV, 4 LiFePO4 100a, xw 6048, Honda eu2000i, iota DLS-54-13, Tesla 3, Leaf, Volt, 4 ton horizontal geothermal, grid tied - Green Bay, WI
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: large batterybank - small solar system

    If you have a charger around, at least give each battery a charge individually. if they have been sitting a while, they are likely low, and need a top - off charge
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

  • tef
    tef Registered Users Posts: 2
    Re: large batterybank - small solar system

    Thank you for the replies.

    I will connect them to three independent parallel strings and switch between them.

    The batteries got disconnected from the ups three weeks ago and their voltages (12.5V) are exactly the same as stated in the data sheet for the correct storage voltage.

    Would you attach the two newer 190Ah batteries to one of the strings, or is this not advisable, even if I only use a small amount of the total capacity?